Synziphosurine
Early Ordovician (Arenigian)
Upper Fezouata Formation
Zagora, Draa Valley, Morocco

26mm side view with rarely seen appendages plus 7mm juvenile on 122mm x 84mm slab.

This is perhaps the earliest known occurrence of synziphosurines which are better known from the Early Silurian to Early Carboniferous.

Here’s an interesting double with one of them being a juvenile.

A synziphosurine is a member of a suborder of arthropods, Synziphosurina, considered to be stem-group xiphosurans. In other words, based on current understanding, they may not be ancestral to xiphosurans (horseshoe crabs) but they are more closely related to their ancestors than to other groups.

Video is an amazing 3D scan of a similar specimen from the Silurian